Generally V-shaped interferometer formed from beamsplitter deployed between geometrically similar prisms

ABSTRACT

An optical device includes two prisms and a beamsplitter configuration. A first of the prisms has a first surface associated with a source and a second surface oblique to the first surface. A second of the prisms has a first surface associated with a detector and a second surface oblique to the first surface. The second surface of the first prism overlaps with the second surface of the second prism to define an interface region that partially extends along at least one of the second surfaces. The prisms are optically attached at the interface region, and the beamsplitter configuration overlies the interface region. A beam emitted by the source propagates through the prisms along two optical paths and reaches the detector as two coherent beams. Beams that propagate along the two optical paths are reflected from the beamsplitter configuration and transmitted by the beamsplitter configuration exactly once.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication No. 62/867,260, filed Jun. 27, 2019, whose disclosure isincorporated by reference in its entirety herein.

TECHNICAL FIELD

The present invention relates to interferometric optical devices andsystems.

BACKGROUND OF THE INVENTION

Interferometers are optical set-ups that are widely used inspectroscopic equipment, spectrometers and spectral imagers to measurethe spectrum of radiation emitted by an object or source. Inspectroscopic applications, the spectrum is generally used to analyzethe physical and chemical characteristics of the object/source thatemits the radiation. There are several known techniques that can be usedto obtain similar information using different optical light manipulationmethods, including, for example, filtering, dispersion, and diffractionthrough periodically treated optical elements.

SUMMARY OF THE INVENTION

The present invention is an interferometric optical device having abeamsplitter configuration deployed between two geometrically similarprisms, preferably two prisms that are offset one with respect to theother and not of the same size.

According to the teachings of an embodiment of the present invention,there is provided optical device. The optical device comprises: a prismassembly including: a first prism comprising a light-transmittingmaterial having a plurality of surfaces including at least a firstsurface associated with a source of light and a second surface obliqueto the first surface, and a second prism comprising a light-transmittingmaterial having a plurality of surfaces including at least a firstsurface associated with a detector and a second surface oblique to thefirst surface of the second prism, the second surface of the first prismis in overlapping relation with the second surface of the second prismto define an interface region of a given length that partially extendsalong at least one of the second surface of the first prism or thesecond surface of the second prism, and the first and second prisms areoptically attached at the interface region; and a beamsplitterconfiguration overlying the interface region, such that an incominglight beam emitted by the source of light propagates through the firstand second prisms along a first optical path and a second optical pathso as to reach the detector as two coherent light beams, and such thatlight beams that propagate from the source of light to the detectoralong each of the first and second optical paths are reflected from thebeamsplitter configuration and transmitted by the beamsplitterconfiguration exactly once.

Optionally, a difference between a length of the first and secondoptical paths varies as a function of an angle of incidence of theincoming light beam due at least in part to the length of the interfaceregion.

Optionally, the source of light is a remote scene that emits radiation.

Optionally, the source of light includes an object that emits lightwaves in response to illumination by a light source.

Optionally, the source of light includes an illumination arrangement,corresponding to the source of light associated with the second surfaceof the first prism, that produces beams of light.

Optionally, the optical device further comprises: an illuminationarrangement corresponding to the source of light associated with thefirst surface of the first prism that produces beams of light.

Optionally, the optical device further comprises: a detector arrangementcorresponding to the detector associated with the second surface of thesecond prism.

Optionally, the optical device further comprises: a scanning arrangementconfigured to change an angle of incidence of light beams, emitted bythe source of light, on the first surface of the first prism.

Optionally, the scanning arrangement includes a rotational mechanismconfigured to rotate at least the prism assembly about an axis ofrotation, and the axis of rotation is parallel to at least one of: i) anedge of the first prism formed by the first surface of the first prismand the second surface of the first prism, or ii) an edge of the secondprism formed by the first surface of the second prism and the secondsurface of the second prism.

Optionally, the axis of rotation passes through the beamsplitterconfiguration.

Optionally, the optical device further comprises a reflective coatingapplied to at least one of the surfaces of at least one of the firstprism or the second prism.

Optionally, the plurality of surfaces of the second prism furtherincludes a third surface, and light beams that propagate from the sourceof light to the detector along the first optical path are reflected oncefrom each of the first and third surfaces of the second prism.

Optionally, at least some of the reflections of the light beams from thefirst and third surfaces of the second prism are reflections by totalinternal reflection.

Optionally, the second surface of the second prism is oblique to thethird surface of the second prism.

Optionally, the plurality of surfaces of the first prism furtherincludes a third surface, and light beams that propagate from the sourceof light to the detector along the second optical path are reflectedonce from each of the first and third surfaces of the first prism.

Optionally, at least some of the reflections of the light beams from thefirst and third surfaces of the first prism are reflections by totalinternal reflection.

Optionally, the second surface of the first prism is oblique to thethird surface of the first prism.

Optionally, the plurality of surfaces of the first prism furtherincludes a third surface, and the plurality of surfaces of the secondprism further includes a third surface, and the light-transmittingmaterial of the first and second prisms have a refractive index greaterthan a refractive index of a medium in which the prism assembly isdeployed so as to define a critical angle such that light beams thatpropagate along the first and second optical paths that are incident onthe first and third surfaces of the first and second prisms at anglesgreater than the critical angle are reflected from the first and thirdsurfaces of the first and second prisms by total internal reflection.

Optionally, the first surface of the first prism is further associatedwith a second detector, and light beams emitted by the source of lightpropagate through the first and second prisms along a third optical pathand a fourth optical path so as to reach the second detector as twocoherent light beams, and light beams that propagate from the source oflight to the second detector along the third optical path are reflectedfrom the beamsplitter configuration exactly twice and are nottransmitted by the beamsplitter configuration, and light beams thatpropagate from the source of light to the second detector along thefourth optical path are transmitted by the beamsplitter configurationexactly twice and are not reflected from the beamsplitter configuration.

Optionally, a difference between a length of the third and fourthoptical paths varies as a function of an angle of incidence of theincoming light beam due at least in part to the length of the interfaceregion.

Optionally, the optical device further comprises an anti-reflectioncoating applied to the first surface of the first prism and the firstsurface of the second prism.

Optionally, the beamsplitter configuration includes a beamsplittercoating applied to at least a portion of at least one of the secondsurface of the first prism or the second surface of the second prism.

Optionally, the beamsplitter configuration includes a thin piece ofmaterial optically attached to, and extending along at least a portionof, at least one of the second surface of the first prism or the secondsurface of the second prism.

Optionally, the beamsplitter configuration is wavelength andpolarization independent.

Optionally, the first and second prisms are triangular prisms.

Optionally, the first and second prisms are right angle prisms.

Optionally, the first and second prisms are mutually geometricallysimilar.

Optionally, the first prism is a mirrored version of the second prism.

Optionally, the first prism is a scaled version of the second prism.

Optionally, the interface region extends along a majority portion of thesecond surface of the first prism and a majority portion of the secondsurface of the second prism, and the majority portions are substantiallyequally sized portions.

Optionally, the interface region extends along a majority portion of thesecond surface of the first prism and a majority portion of the secondsurface of the second prism, and the majority portions are unequallysized portions.

Optionally, the interface region extends along a majority portion of thesecond surface of the first or second prism, and the interface regionextends along substantially the entirety of the second surface of thesecond or first prism.

There is also provided according to an embodiment of the teachings ofthe present invention an optical device. The optical device comprises: aprism assembly including: a first prism comprising a light-transmittingmaterial having a plurality of surfaces including at least a firstsurface associated with a source of light and a second surface obliqueto the first surface, and a second prism comprising a light-transmittingmaterial having a plurality of surfaces including at least a firstsurface associated with a detector and a second surface oblique to thefirst surface of the second prism, the second surface of the first prismis in overlapping relation with the second surface of the second prismto define an interface region and such that at least one of a portion ofthe second surface of the first prism extends beyond the second surfaceof the second prism, or a portion of the second surface of the secondprism extends beyond the second surface of the first prism, by a givenoffset amount, and the first and second prisms are optically attached atthe interface region; and a beamsplitter configuration overlying theinterface region, such that an incoming light beam emitted by the sourceof light propagates through the first and second prisms along a firstoptical path and a second optical path so as to reach the detector astwo coherent light beams, and such that light beams that propagate fromthe source of light to the detector along each of the first and secondoptical paths are reflected from the beamsplitter configuration andtransmitted by the beamsplitter configuration exactly once.

Optionally, a minority portion of the second surface of the first prismextends beyond the second surface of the second prism by a first givenoffset amount, and a minority portion of the second surface of thesecond prism extends beyond the second surface of the first prism by asecond given offset amount.

Optionally, the first given offset amount is substantially equal to thesecond given offset amount.

Optionally, the first given offset amount is unequal to the second givenoffset amount.

Optionally, a minority portion of exactly one of the second surface ofthe first prism or the second surface of the second prism extends beyondthe second surface of the second prism or the second surface of thefirst prism by a given offset amount.

There is also provided according to an embodiment of the teachings ofthe present invention a method of forming an interferogram. The methodcomprises:

deploying a prism assembly having a beamsplitter configuration in anoptical path from a source of light to a detector, the prism assemblyincludes a first prism and a second prism, the first prism comprises alight-transmitting material having a plurality of surfaces including atleast a first surface associated with the source of light and a secondsurface oblique to the first surface, and the second prism comprises alight-transmitting material having a plurality of surfaces including atleast a first surface associated with the detector and a second surfaceoblique to the first surface of the second prism, and the second surfaceof the first prism is in overlapping relation with the second surface ofthe second prism to define an interface region of a given length thatpartially extends along at least one of the second surface of the firstprism or the second surface of the second prism, and the beamsplitterconfiguration overlies the interface region and the first and secondprisms are optically attached at the interface region; varying an angleof incidence of light beams, emitted by the source of light, to one ofthe surfaces of the prism assembly; and while varying the angle ofincidence, detecting, by the detector, light beams emitted by the sourceof light, each light beam emitted by the source of light propagatesthrough the first and second prisms along a first optical path and asecond optical path so as to reach the detector as two coherent lightbeams, and each light beam that propagates from the source of light tothe detector along each of the first and second optical paths isreflected from the beamsplitter configuration and transmitted by thebeamsplitter configuration exactly once, and a difference between alength of the first and second optical paths varies as a function of theangle of incidence of each incoming light beam due at least in part tothe length of the interface region.

Optionally, the method further comprises: deploying a second detector inassociation with the first surface of the first prism; and while varyingthe angle of incidence, detecting, by the second detector, light beamsemitted by the source, each light beam emitted by the source of lightpropagates through the first and second prisms along a third opticalpath and a fourth optical path so as to reach the second detector as twocoherent light beams, and each light beam that propagates from thesource of light to the second detector along the third optical path isreflected from the beamsplitter configuration exactly twice and is nottransmitted by the beamsplitter configuration, and each light beam thatpropagates from the source of light to the second detector along thefourth optical path is transmitted by the beamsplitter configurationexactly twice and is not reflected from the beamsplitter configuration.

Optionally, the varying the angle of incidence includes rotating atleast the prism assembly about an axis of rotation.

Optionally, the axis of rotation passes through the beamsplitterconfiguration.

Optionally, the axis of rotation is parallel to at least one of: i) anedge of the first prism formed by the first surface of the first prismand the second surface of the first prism, or ii) an edge of the secondprism formed by the first surface of the second prism and the secondsurface of the second prism.

There is also provided according to an embodiment of the teachings ofthe present invention an optical device. The optical device comprises: afirst substantially planar reflective surface associated with a sourceof light; a second substantially planar reflective surface; a thirdsubstantially planar reflective surface associated with a detector; afourth substantially planar reflective surface; and a substantiallyplanar beamsplitter configuration, the planes of the first planarreflective surface, the second planar reflective surface, and thebeamsplitter configuration intersect to form a first prismaticstructure, and the planes of the third planar reflective surface, thefourth planar reflective surface, and the beamsplitter configurationintersect to form a second prismatic structure, and the plane of thebeamsplitter configuration and the plane of the first reflective surfaceintersect to form a first line of intersection, and the plane of thebeamsplitter configuration and the plane of the second reflectivesurface intersect to form a second line of intersection, and the planeof the beamsplitter configuration and the plane of the third reflectivesurface intersect to form a third line of intersection, and the plane ofthe beamsplitter configuration and the plane of the fourth reflectivesurface intersect to form a fourth line of intersection, and the firstand second prismatic structures are in overlapping relation along theplane of the beamsplitter configuration such that at least one of apoint on the fourth line of intersection extends beyond a colinear pointon the second line of intersection, or a point on the first line ofintersection extends beyond a colinear point on the third line ofintersection by a given offset amount, and a light beam emitted by thesource of light propagates to the detector along a first optical pathand a second optical path so as to reach the detector as two coherentlight beams, and light beams that propagate from the source of light tothe detector along the first optical path are transmitted once by thebeamsplitter configuration, and are reflected once by the beamsplitterconfiguration, the first reflective surface, and the second reflectivesurface, and light beams that propagate from the source of light to thedetector along the second optical path are transmitted once by thebeamsplitter configuration, and are reflected once by the beamsplitterconfiguration, the third reflective surface, and the fourth reflectivesurface.

Unless otherwise defined herein, all technical and/or scientific termsused herein have the same meaning as commonly understood by one ofordinary skill in the art to which the invention pertains. Althoughmethods and materials similar or equivalent to those described hereinmay be used in the practice or testing of embodiments of the invention,exemplary methods and/or materials are described below. In case ofconflict, the patent specification, including definitions, will control.In addition, the materials, methods, and examples are illustrative onlyand are not intended to be necessarily limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention are herein described, by wayof example only, with reference to the accompanying drawings. Withspecific reference to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

Attention is now directed to the drawings, where like reference numeralsor characters indicate corresponding or like components. In thedrawings:

FIG. 1 is a schematic isometric view of an optical device having twoprisms translated one with respect to the other and a beamsplitterdeployed therebetween, constructed and operative according to anembodiment of the present invention;

FIG. 2 is a schematic exploded isometric view to show the details of theprisms and the beamsplitter of the optical device of FIG. 1;

FIG. 3 is a plan view of the optical device of FIG. 1;

FIG. 4 is a schematic partially exploded plan view to show the detailsof the prisms and beamsplitter of the optical device of FIGS. 1 and 3;

FIG. 5 is a schematic plan view showing the details of an interfaceregion between the prisms of FIGS. 1 and 3;

FIG. 6 is a schematic plan view of the optical device of FIG. 3,modified to show a source of light and a detector, and to show thetraversal of light rays, via the prisms and the beamsplitter, from thesource of light to the detector along a first optical path;

FIG. 7 is a schematic plan view of the optical device of FIG. 3,modified to show a source of light and a detector, and to show thetraversal of light rays, via the prisms and the beamsplitter, from thesource of light to the detector along a second optical path;

FIG. 8 shows the traversal of the light rays illustrated in FIGS. 6 and7 overlaid in a single drawing;

FIG. 9 is a schematic plan view of an optical system including theoptical device of FIGS. 6-8, a scanning arrangement, and a processingunit, according to an embodiment of the present invention;

FIG. 10 is a schematic plan view of the optical device of FIG. 3,modified to show a source of light and a second detector, and to showthe traversal of light rays, via the prisms and the beamsplitter, fromthe source of light to the second detector along a third optical path;

FIG. 11 is a schematic plan view of the optical device of FIG. 3,modified to show a source of light and a second detector, and to showthe traversal of light rays, via the prisms and the beamsplitter, fromthe source of light to the second detector along a fourth optical path;

FIG. 12 is a schematic plan view of an optical device having two prismsand a beamsplitter deployed therebetween, with one of the prisms being ascaled version of the other prism and the two prisms translated one withrespect to the other, constructed and operative according to anotherembodiment of the present invention;

FIG. 13 is a schematic exploded plan view to show the details of theinterface region between the prisms of FIG. 12;

FIG. 14 is a schematic plan view of the optical device of FIG. 12,modified to show a source of light and a detector and sample raystraversing the prisms along two optical paths;

FIG. 15 is a schematic plan view of an optical device having two prismsand a beamsplitter deployed therebetween, with one of the prisms being ascaled version of the other prism and the two prisms positioned one withrespect to the other along an interface region, constructed andoperative according to another embodiment of the present invention;

FIG. 16 is a schematic exploded plan view to show the details of theinterface region between the prisms of FIG. 15;

FIG. 17 is a schematic plan view of an optical device having two prismsand a beamsplitter deployed therebetween, with one of the prisms being ascaled version of the other prism and the two prisms positioned one withrespect to the other along an interface region, constructed andoperative according to a further embodiment of the present invention;

FIG. 18 is a schematic plan view of an optical device similar to theoptical device of FIG. 14, but with the solid material of the prismsreplaced with air; and

FIG. 19 is a schematic plan view of an optical device, based on theoptical device of FIG. 12, having cut-off corners.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention provide interferometric opticaldevices and systems based on two geometrically similar prisms having abeamsplitter configuration deployed between the prisms. In certainembodiments, the interferometer has a general cross-sectional v-shape.

The principles and operation of the optical devices and systemsaccording to present invention may be better understood with referenceto the drawings accompanying the description.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways. Initially, throughout this document, references are madeto directions such as, for example, front and rear, upper and lower, topand bottom, and the like. These directional references are exemplaryonly to illustrate the invention and embodiments thereof.

Referring now to the drawings, FIGS. 1-8 illustrate various views of anoptical device, generally designated 10, and corresponding componentsthereof, constructed and operative according to various aspects of thepresent disclosure. In general terms, the optical device 10 includes twotriangular prisms, namely a first prism 12 and a second prism 22, eachformed from a light-wave transmitting material, and a beamsplitterconfiguration 20 deployed between the first prism 12 and the secondprism 22, to provide interferometric functionality. The interferometricfunctionality is enabled by prisms 12, 22 that are mutuallygeometrically similar such that the prisms 12, 22 would be perfectlysymmetric about a plane of symmetry if not for scaling and/ortranslating of one of the prisms with respect to the other. Within thecontext of this document, two geometric objects (three-dimensional andmade of planar surfaces) are considered to be geometrically similar ifone can be obtained from the other by scaling (i.e., enlarging orreducing) one or more of the surfaces (either independently oruniformly) of one of the objects, possibly with one or more ofadditional translation, rotation and reflection, without changing theangles between the surfaces of each of the objects. As will becomeapparent, the geometric similarity of the two prisms 12, 22 providesparticular advantages when scanning the optical path difference(OPD)—defined as the difference in length between two optical pathsthrough the prisms 12, 22—by way of changing the angle of incidence oflight rays (emitted by a source of light) measured with respect to thenormal relative to the incident surface of one of the prisms 12 across afield of view of the optical device 10. For a given optical path througha medium, the optical path length is generally defined as the pathintegral of the geometric path length multiplied by the local index ofrefraction of the medium along the path.

Bearing the above in mind, the first prism 12 has a number of planarexternal surfaces, including the following three main surfaces: a firstsurface 14 associated with a source of light, a second surface 16, and athird surface 18. The first surface 14 serves a light-wave entrance forincoming light waves (schematically represented as light rays) from thesource of light, as will subsequently be discussed in greater detail.The apex angle α is defined as the angle between the first surface 14and the second surface 16, and is less than 90°.

In the present embodiment, the first prism 12 is a right-angledtriangular prism, wherein the first surface 14 and the third surface 18are joined at a right angle and the second surface 16 is oblique (andacute) to both the first surface 14 and the third surface 18. It isnoted that the optical devices of the present disclosure are preferablybased on right-angled (or approximately right-angled) triangular prisms.Right-angled prisms provide certain advantages over non-right-angledprism, for example, with respect to the manufacturing process of theprism assembly 30, as right-angle cuts are typically easier to fabricatethan non-right-angled prisms when using conventional optical devicemanufacturing machinery. However, non-right-angled prisms, i.e., prismshaving a largest internal angle not equal to 90° are also contemplatedherein, and may have advantages in certain applications. Generallyspeaking, the mathematical relationships between the various prismparameters may vary slightly (as will be discussed in subsequentsections of the present disclosure), but the overall function of theoptical set-up remains the same regardless of these parameters.Therefore, the optical devices according to the embodiments of thepresent disclosure should not be limited in scope to right-angledtriangular prisms.

The first prism 12 also includes additional external surfaces, includinga triangular shaped front surface 19 that is joined to the threesurfaces 14, 16, 18, and a triangular shaped rear surface (not shown)parallel to, and opposite from, the front surface 19. In the presentembodiment, the three surfaces 14, 16, 18 are rectangular surfaces, andin certain embodiments the third surface 18 is square shaped. In allembodiments, the surfaces 19 and 29 are coplanar (i.e., they lay in thesame plane), and the rear surfaces opposite the surfaces 19 and 29 arecoplanar. Parenthetically, since the surfaces 19, 29 and their opposingsurfaces do not play a significant role in the interferometric process(other than that the prism thickness should be big enough to contain theoptical beams propagating along their respective optical paths), thiscoplanarity is not critical and is not necessary for the invention. Thesurface 19 and its opposing surface are preferably parallel to eachother and orthogonal to the surfaces 14 and 18, and the surface 29 andits opposing surface are preferably parallel to each other andorthogonal to the surfaces 24 and 28, however, this parallelism andorthogonality is not a strict requirement. In fact, the surfaces 19, 29and their opposing surfaces may be non-planar surfaces.

The second prism 22 has a number of planar external surfaces, includingthe following three main surfaces: a first surface 24 associated with adetector, a second surface 26, and a third surface 28. The first surface24 serves a light-wave exit surface for light waves to exit the secondprism 22 to the detector, as will subsequently be discussed in greaterdetail. In the present embodiment, the second prism 22, like the firstprism 12, is a right-angled triangular prism, wherein the first surface24 and the third surface 28 are joined at a right angle and the secondsurface 26 is oblique to both the first surface 24 and the third surface28.

In certain embodiments, the two prisms 12, 22 are of the same size andare mirror images of each other but are translated (i.e., shifted) onewith respect to the other along the length of the second surfaces 16,26. In such embodiments, the prisms 12, 22 would be perfectly symmetricabout a plane of symmetry extending along second surfaces 16, 26 if notfor the translation. In other embodiments, the second prism 22 is ascaled and mirror imaged version of the first prism 12 and the prisms12, 22 may also be translated one with respect to the other along thesecond surfaces 16, 26. In such embodiments, the prisms 12, 22 would beperfectly symmetric about a plane of symmetry extending along secondsurfaces 16, 26 if not for the scaling and translation. In all of theaforementioned embodiments, since the two prisms 12, 22 aregeometrically similar, the apex angle α is also the angle between thefirst surface 24 and the second surface 26.

The second prism 22 also includes additional external surfaces,including a triangular shaped front surface 29 that is joined to thethree surfaces 24, 26, 28, and a triangular shaped rear surface (notshown) parallel to, and opposite from, the front surface 29. As shouldbe understood by the property of geometric similarity, the threesurfaces 24, 26, 28 are rectangular surfaces, and in certain embodimentsthe third surface 18 is square shaped.

At least one of the prisms 12, 22 is provided on the hypotenuse side(the second surface 16 or the second surface 26) with a coating to forma beamsplitter forming at least part of a beamsplitter configuration 20.In the non-limiting example illustrated in FIG. 4, the coating isprovided on the hypotenuse side of the first prism 12 (i.e., on thesecond surface 16). Note that the thickness of the beamsplitterconfiguration 20 illustrated in FIG. 4 is exaggerated for clarity ofillustration. Preferably, the beamsplitter configuration 20 isconfigured to transmit approximately half of the incoming light andreflect approximately half of the incoming light (ideally independentlyof angle of incidence and polarization). In certain embodiments, thehypotenuse sides of the two prisms 12, 22 are cemented to each other, toform a cemented prism assembly 30 having the beamsplitter configuration20 fixedly deployed between the two hypotenuse sides (i.e., the surfaces16, 26). In other embodiments, the hypotenuse sides are simplyjuxtaposed, or placed in good mechanical contact with each other,optionally by means of an additional transparent liquid or gel toimprove optical contact between the prisms 12, 22 and to eliminate smalldetrimental air pockets in the interface region between the prisms 12,22.

The coating can be provided on the hypotenuse side of at least one ofthe prisms 12, 22 in various ways. In one non-limiting example, thecoating can be applied directly on a portion (preferably a majorityportion) or the entirety of the hypotenuse side of one or both of thetwo constituent prisms 12, 22. In another non-limiting example, a thinpiece of material, such as, for example, a sheet, foil, or thin glassplate, that has a beamsplitter coating deposited thereon and extendsalong a portion (preferably a majority portion) or the entirety of thehypotenuse sides of the two constituent prisms 12, 22, can be cementedbetween the hypotenuse sides of the two constituent prisms 12 to formthe unitary prism assembly 30.

Parenthetically, the beamsplitter configuration 20 is preferablyconfigured to reflect and transmit a proportion of light incident to thesurface of the beamsplitter configuration independent of wavelength andpolarization direction of the incident light. However, as will bediscussed in subsequent sections of the present disclosure, the prisms12, 22 may be constructed from materials which are transparent to lightin particular regions of the electromagnetic spectrum, such as thevisible (400 to 800 nanometer) range, the NIR, or the near infrared,usually referring to the 0.8 to 2.5 micron region, the medium wavelengthinfrared (MWIR) region, usually referring to the 3 to 5 micron range,and/or the long-wavelength infrared (LWIR) region, usually referring tothe 7 to 14 micron region of the spectrum. Accordingly, light from theentire spectrum may not reach the beamsplitter configuration surface.

In all of the embodiments of the present disclosure, the second surfaces16, 26 are in overlapping relation with each other (i.e., they mutuallyoverlap) to define an interface region. The interface region is atwo-dimensional region having a given width measured in the dimension ofthe edge 15 that joins together the surface 16 and the surface 18 (i.e.,the direction into the plane of the paper), and a given length measuredin the dimension of the edge 13 that joins together the surface 16 andthe surface 19 (and equivalently the edge that joins together thesurface 26 and the surface 29) which in the context of the drawings isthe vertical dimension. The given length of the interface region extendspartially along at least one of the second surfaces 16, 26. In certainpreferred embodiments, the given length of the interface region extendsalong a majority of at least one of the second surfaces 16, 26. Withinthe context of this document, extending partially along a surfacegenerally refers to extending along at least part of the surface butextending along less than the entirety of the surface. The interfaceregion 31 is the region at which the two prisms 12, 22 are cementedtogether (or juxtaposed or placed in mechanical contact with each other)to form the unitary prism assembly 30, and may also be referred to as acontact surface or interface plane between the two prisms 12, 22. Thebeamsplitter configuration 20 overlies the entirety of the interfaceregion 31, and is generally aligned with the interface region along thewidth dimension.

As will be discussed, in certain embodiments (e.g., FIGS. 1-11) theinterface region extends partially along equal portions (equal majorityportions in the illustrated example) of the second surfaces 16, 26,while in other embodiments (e.g., FIGS. 12-14) the interface regionextends partially along unequal portions (unequal majority portions inthe illustrated example) majority portions of the second surfaces 16,26, and yet in other embodiments (e.g., FIGS. 15-17) the interfaceregion extends along a majority portion of one of the second surfaces16, 26 and extends along the entirety of the other of the secondsurfaces 16, 26.

Analogously, the second surfaces 16, 26 mutually overlap such that aportion of at least one of the surfaces 16, 26 extends beyond the otherof the surfaces 16, 26 by a given offset amount along the dimension ofthe edge that joins together the surface 16 and the surface 19 (andequivalently the edge that joins together the surface 26 and the surface29). In certain preferred embodiments, a minority portion of at leastone of the surfaces 16, 26 extends beyond the other of the surfaces 16,26. As will be discussed, in certain embodiments (e.g., FIGS. 1-14) thesecond surfaces 16, 26 mutually overlap such that a portion (a minorityportion in the illustrated example) of the surface 16 extends beyond thesurface 26 by a first given offset amount and a portion (a minorityportion in the illustrated example) of the surface 26 extends beyond thesurface 16 by a second given offset amount. In some embodiments (e.g.,FIGS. 1-11), the first and second given offset amounts are equal, i.e.,the amount by which the surface 16 extends beyond the surface 26 is thesame as the amount by which the surface 26 extends beyond the surface16. In other embodiments (e.g., FIGS. 12-14), the first and second givenoffset amounts are unequal, i.e., the amount by which the surface 16extends beyond the surface 26 is less than or greater than the amount bywhich the surface 26 extends beyond the surface 16. In yet otherembodiments (e.g., FIGS. 15-17), the second surfaces 16, 26 mutuallyoverlap such that a minority portion of only one of the surfaces 16, 26extends beyond the other of the surfaces 16, 26 by a given offsetamount, i.e., the surface 16 extends beyond the surface 26 by a givenoffset amount but the surface 26 does not extend beyond the surface 16,or the surface 26 extends beyond the surface 16 by a given offset amountbut the surface 16 does not extend beyond the surface 26. It is notedthat in the accompanying drawings, the size of the offset amount(s)is/are exaggerated for clarity of illustrating the operation of theoptical devices of the present disclosure.

By further analogy, the second surfaces 16, 26 mutually overlap suchthat at least one of the edges of one of the prisms 12, 22 extendsbeyond a corresponding one of the edges of the other prism by a givenoffset amount along the dimension of the edge that joins together thesurface 16 and the surface 19 (and equivalently the edge that joinstogether the surface 26 and the surface 29).

Within the context of this document, the majority portion of a surfacegenerally refers to the contiguous portion of the surface that covers atleast half (50%) of the length of the surface but not the entire lengthof the surface. Similarly, within the context of this document, theminority portion of a surface generally refers to the contiguous portionof the surface that covers at least some, but less than half (50%), ofthe length of the surface.

Looking at the optical device 10 of FIGS. 1-8, the second surfaces 16,26 mutually overlap to define an interface region 31 of a given lengththat extends along equal portions (equal majority portions in theillustrated example) of the second surfaces 16, 26. The amount ofoverlap between the second surfaces 16, 26 effects a translation (i.e.,shift) of one of the prisms with respect to the other along the secondsurfaces 16, 26 by a given offset amount 32 (also referred tointerchangeably herein as a shift amount or translation amount). Withoutloss of generality, the offset amount 32 is the amount by which one ofthe surfaces 16, 26 extends beyond the other of the surfaces 16, 26along the dimension of the edge 13 that joins together the surface 16and the surface 19 (and equivalently the edge that joins together thesurface 26 and the surface 29). The offset amount 32 can be equivalentlydefined as the distance between a point on the edge 15 of the firstprism 12 and a point on the edge 25 of the second prism 22, where theedge 15 joins together the surface 16 and the surface 18, and the edge25 joins together the surface 26 and the surface 28. The points on theedges 15, 25 between which the offset amount 32 is measured arecoplanar. Analogously, the offset amount 32 can be defined as thedistance (along the dimension of the edge that joins together thesurface 16 and the surface 19) by which the edge 25 or 15 extends beyondthe edge 15 or 25.

In the present embodiment in which the two prisms 12, 22 are of the samesize and are mirror images of each other that are translated along thelength of the surfaces 16, 26, the surface 16 extends beyond the surface26 (at the top of the prism assembly 30) and the surface 26 extendsbeyond the surface 16 (at the bottom of the prism assembly 30) by thesame offset amount 32. Accordingly, the offset amount 32 can equally bedefined as the distance between a point on the edge 27 of the secondprism 22 and a point on the edge 17 of the second prism 12, where theedge 17 joins together the surface 14 and the surface 16, and the edge27 joins together the surface 24 and the surface 26. The points on theedges 17, 27 between which the offset amount 32 is measured arecoplanar. Analogously, the offset amount 32 can be defined as thedistance (along the dimension of the edge that joins together thesurface 16 and the surface 19) by which the edge 17 or 27 extends beyondthe edge 27 or 17. Parenthetically, the offset amount 32 iscomplementary to the length of the interface region 31 (it is thedifference between the length of edge 13 and the length of the interfaceregion along the surfaces 16 and 26). In other words, an interfaceregion 31 of large length corresponds to a small relative shift betweenthe two prisms 12, 22 (i.e., a small offset amount 32), whereas aninterface region 31 of small length corresponds to a large relativeshift between the two prisms 12, 22 (i.e., a large offset amount 32).

The prisms 12, 22 are preferably constructed from a light-wavetransmitting material, suitable for the desired application of theoptical device 10, and having a refractive index that is high enoughsuch that light waves propagating within the prisms 12, 22 at anglesgreater than a critical angle (measured relative to the normal to theincident surface and defined by the refractive index of the prisms 12,22 and the refractive index of the medium in which the prism assembly 30is deployed, e.g., air), are trapped within the prisms 12, 22 by totalinternal reflection from the first and third surfaces 14, 18, 24, 28. Aswill be discussed in subsequent sections of the present disclosure, inparticular with reference to FIGS. 6-8, the specific design choice ofthe internal angles of the prisms 12, 22 and the material from which theprisms 12, 22 are constructed play an essential role in determining thepropagation path of light through each of the prisms 12, 22.

The surfaces 14, 18, 24, 28 may alternatively be coated with aspecularly reflective (for example metal such as aluminum or gold, orother approximately wavelength independent reflectors) coating in orderto achieve high reflection of light rays. Angularly selective reflective(ASR) coatings are also contemplated herein, so that the lightpropagates within desired angular ranges. Note that one of the prisms12, 22 may be constructed from the high index material and the other ofthe prisms 12, 22 may be coated with a specularly reflective or an ASRcoating.

With particular reference to FIGS. 6-8, there is shown the traversal oflight rays through the prism assembly 30 when the prism assembly 30 isdeployed in an optical path between a source of light 34 and a detectorarrangement 36 (referred to hereinafter as detector 36). The source oflight 34 emits light beams, where each beam can be considered agenerally planar wavefront that enters the prism assembly 30 fromdifferent directions through one of the surfaces of the prism assembly30, which by way of illustration is the first surface 14 of the firstprism 12. A single beam of light emitted by the source of light 34propagates through the prism assembly 30 along two different opticalpaths resulting in two coherent beams at the output of the prismassembly 30 that impinge on the detector 36. The coherent beams thatreach the detector 36 are used to build up an interferogram by way ofscanning of the optical path difference (via, for example, rotation ofthe prism assembly 30 and/or changing entrance direction of the beamemitted by the source of light 34).

Parenthetically, the source of light 34 can be a manufactured source ora natural scene, depending on the application of the optical device 10.In a particularly useful application, the optical device 10 is used forspectral imaging of a remote scene, where the radiation from every scenepixel can be imaged simultaneously by a multi-element detector. In otherapplications, the manufactured source is a wide band or monochromaticsource, used to illuminate a sample, in order to analyze the spectralcharacteristics of the sample. In even further applications the sourceitself is the object of the spectral analysis, rendered possible by thepresent invention. In the above-mentioned remote scene spectral imagingexample, the spectral information for every pixel is obtainedsimultaneously by acquiring the signals through rotation or translationof the prism and the multi-element detector 36, or by other scanningmeans known by the person skilled in the art. In other examples thedetector is made of a single element and the information is gathered asfunction of time by scanning the entrance angle of the source radiationwith respect to the first surface 14 of the prism 12. A spectral regionof notable relevance for the purpose of the present invention is theinfrared region, particularly the MWIR and the LWIR regions of theelectromagnetic spectrum. In such applications, the prisms 12, 22 areconstructed from a material that is transparent to light havingwavelengths in the above regions (3-5 μm or 8-15 μm, respectively), forexample zinc selenide (ZnSe), which has an almost wavelength-independentrefractive index of approximately 2.4 in the above region. When theprism assembly 30 is deployed in air, the resultant critical angle forlight in this wavelength region is approximately 24.6°. Constructing theprisms 12, 22 from other materials, such as germanium dioxide, which hasa refractive index of approximately 1.65, is also contemplated. In sucha construction, when the prism assembly 30 is deployed in air, theresultant critical angle is approximately 37.3°.

In the other potential applications mentioned above, the optical device10 may be used to determine the spectral characteristics of anillumination arrangement composed of, for example, one or more LEDs orother types of light sources, the incoming light waves to the prismassembly 30 are received directly from the illumination arrangement. Insuch applications the source of light 34 is the illumination arrangementitself. In other applications, the optical device 10 may be used todetermine the spectral characteristics of an object that emits (via, forexample, diffusion or reflection) light waves in response toillumination by an illumination arrangement. In such applications, theobject to be analyzed is the light waves emitting object, and the sourceof light 34 is deployed in such a way so as to illuminate the lightwaves emitting object.

Although not shown in the drawings, a lens (or lenses) may be deployedin the optical path between the source of light 34 and the surface 14 soas to gather or direct the light from the source of the light 34 towardthe surface 14. Another lens (or lenses) may be deployed in the opticalpath between the surface 24 and the detector 36 so as to focus the lightexiting the second prism 22 onto the plane of the detector 36.

Referring first to FIG. 6, there is shown the traversal of a beam fromthe source of light 34 to the detector 36 along a first optical path(having a corresponding first optical path length) through the prismassembly 30. The light beam, represented schematically in FIG. 6 as asample light ray 50 a, is incident to the first surface 14 at anincident angle of γ (where the incident angle is measured relative tothe normal to the surfaced 14, shown by the dotted line crossing thesurface 14). It is noted that the light ray 50 a is one of multiple raysthat span the beam. It is further noted that the beam may be one of manybeams that is incident on the first surface 14, where each beam isspanned by multiple light rays that may or may not be parallel to thelight rays of other beams.

The incident light ray 50 a is transmitted by the first surface 14. Thetransmitted light ray is designated as 50 b. When the incident light ray50 a is incident to the surface 14 at an oblique angle, the light ray 50a is refracted upon entering the prism 12 such that the refractedtransmitted light ray 50 b propagates at an angle of ft (relative to thenormal to the surface 14). In order to minimize intensity loss duringtransmission of the light ray 50 a through the first surface 14, thefirst surface 14 is preferably coated with an anti-reflective coating.The transmitted light ray 50 b impinges on the beamsplitterconfiguration 20 where a proportion of the intensity of the light ray 50b is transmitted by the beamsplitter configuration 20, and is designatedas light ray 50 c. Preferably the proportion of the transmittedintensity is approximately 50% of the intensity. The transmitted lightray 50 c impinges on the first surface 24 of the second prism 22 at anangle greater than the critical angle such that it is totally internallyreflected as light ray 50 d. The light ray 50 d propagates toward thethird surface 28 and impinges on the third surface 28 at an anglegreater than the critical angle such that it is totally internallyreflected as light ray 50 e.

Parenthetically, it is noted that in alternative embodiments in whichthe surfaces 24, 28 are coated with an ASR coating, the reflections ofthe light rays 50 c and 50 d at the respective surfaces 28 and 24 aredue to the specularly reflecting or ASR coating and not total internalreflection. It is further noted that if the source of light 34 ispositioned such that the light ray 50 b impinges on the beamsplitterconfiguration 20 at a region closer to the upper portion of theinterface region 31 (i.e., far from the apex of the prisms 12, 22), theorder of reflection at the surfaces 24, 28 may be reversed.Specifically, the transmitted light ray 50 c may be reflected (by totalinternal reflection or the ASR coating) at the third surface 28 toproduce the light ray 50 d, whereupon the light ray 50 d is reflected atthe first surface 24 (by total internal reflection or the specularlyreflecting or the ASR coating) to produce the light ray 50 e.

The light ray 50 e propagates toward the beamsplitter configuration 20where a proportion of the intensity of the light ray 50 e is reflectedby the beamsplitter configuration 20, and is designated as light ray 50f. In the preferred embodiment in which the beamsplitter configuration20 transmits approximately 50% of the intensity of incident light, thebeamsplitter configuration 20 also reflects approximately 50% of theintensity of incident light.

The light ray 50 f exits the second prism 22 via transmission by thefirst surface 24 of the second prism 22. The transmitted light ray isdesignated as 50 g. When the light ray 50 f is incident to the surface24 at an oblique angle, the light ray 50 f is refracted upon exiting theprism 22 such that the light ray 50 g propagates at an angle of γ(relative to the normal to the surface 24), whereupon the light ray 50 greaches the detector 36. It is noted that in situations in which theprisms 12, 22 are not right-angled prisms, but are still geometricallysimilar prisms, the above description of light propagation along thefirst optical path with respect to right-angled prisms holds except thatthe angle at which the beam exits through the surface 24 is γ′, thisangle being different from the incident angle γ.

As can be seen from FIG. 6, the light that propagates from the source oflight 34 to the detector 36 along the first optical path undergoesexactly one reflection and one transmission by the beamsplitterconfiguration 20.

FIG. 7 shows the traversal of the same beam emitted by the source oflight 34 in FIG. 6 to the detector 36 along a second optical path(having a corresponding second optical path length different from thefirst optical path length) through the prism assembly 30. The secondoptical path follows the trajectory of the light that corresponds to theproportion of the light ray 50 b that is reflected by the beamsplitterconfiguration 20. The light beam, represented schematically in FIG. 7 asa sample light ray 52 a (which in this case is the same as the light ray50 a), is transmitted by the first surface 14, and is designated aslight ray 52 b (which is the same as the light ray 50 b). Thetransmitted light ray 52 b impinges on the beamsplitter configuration 20where a proportion of the intensity of the light ray 52 b is reflectedby the beamsplitter configuration 20, and is designated as light ray 52c.

The light ray 52 c impinges on the first surface 14 of the first prism12 at an angle greater than the critical angle such that it is totallyinternally reflected as light ray 52 d. The light ray 52 d propagatestoward the third surface 18 and impinges on the third surface 18 at anangle greater than the critical angle such that it is totally internallyreflected as light ray 52 e.

Parenthetically, it is noted that in alternative embodiments in whichthe surfaces 14, 18 are coated with a specularly reflecting or an ASRcoating, the reflections of the light rays 52 c and 52 d at therespective surfaces 18 and 14 are due to the specularly reflecting orASR coating and not total internal reflection. It is further noted thatif the source of light 34 is positioned such that the light ray 52 bimpinges on the beamsplitter configuration 20 at a region closer to theupper portion of the interface region 31 (i.e., far from the apex of theprisms 12, 22), the order of reflection at the surfaces 24, 28 may bereversed. Specifically, the transmitted light ray 52 c may be reflected(by total internal reflection or the ASR coating) at the third surface18 to produce the light ray 52 d, whereupon the light ray 52 d isreflected at the first surface 14 (by total internal reflection or theASR coating) to produce the light ray 52 e.

The light ray 52 e propagates toward the beamsplitter configuration 20where a proportion of the intensity of the light ray 52 e is transmittedby the beamsplitter configuration 20, and is designated as light ray 52f. The light ray 52 f exits the second prism 22 via transmission by thefirst surface 24 of the second prism 22. The transmitted light ray isdesignated as 52 g. When the light ray 52 f is incident to the surface24 at an oblique angle, the light ray 52 f is refracted upon exiting theprism 22 such that the light ray 52 g propagates at an angle of γ(relative to the normal to the surface 24), whereupon the light ray 52 greaches the detector 36. Similarly, it is noted that in situations inwhich the prisms 12, 22 are not right-angled prisms, but are stillgeometrically similar prisms, the above description of light propagationalong the second optical path with respect to right-angled prisms holdsexcept that the angle at which the beam exits through the surface 24 isγ′, different from the incident angle γ.

As can be seen from FIG. 7, the light that propagates from the source oflight 34 to the detector 36 along the second optical path undergoesexactly one reflection and one transmission by the beamsplitterconfiguration 20.

As is known to those of skill in the art, a relationship exists betweenthe angle of incidence of the incoming light rays to the varioussurfaces of the prisms 12, 22 and the internal angles of the prisms 12,22. For example, for an incoming light ray that is incident on the firstsurface 14 at an arbitrary oblique incident angle of θ₁ (measuredrelative to the normal to the first surface 14), the transmitted lightray (e.g., the light ray 52 b) is refracted so as to propagate at anangle of:

$\theta_{2} = {\sin^{- 1}\left( \frac{\eta_{1}*\sin\;\theta_{1}}{\eta_{2}} \right)}$where η₂ is the refractive index of the material of the prism 12, and η₁is the refractive index of the medium in which the prism assembly 30 isdeployed (η₁ is approximately 1 when the prism assembly 30 is deployedin air).

The angle θ₂ at which the light ray 52 b propagates is likewise measuredrelative to the normal to the first surface 14. The angle of incidenceθ₃ of the light ray 52 b, measured relative to the normal to the surfaceof the beamsplitter configuration 20 (which is equivalently the secondsurface 16), is given by:

$\theta_{3} = {{{90} - \delta + \theta_{2}} = {{90} - \delta + {\sin^{- 1}\left( \frac{\eta_{1}*\sin\;\theta_{1}}{\eta_{2}} \right)}}}$where δ is the angle between the second surface 16 and the third surface18. Note for non-right-angled prisms, the value of 90 in the precedingequation is replaced by the corresponding maximum internal angle of theprisms (i.e., the angle between the first surface 14 and the thirdsurface 18).

The angles of incidence (measured relative to the incident surface ofthe relevant prism 12, 22) of the remaining light rays in thepropagating (i.e., optical) path to the detector 36 through the prismassembly 30 can be similarly computed using geometry, as is known tothose skilled in the art.

FIG. 8 shows the propagation of the light rays 50 a-50 g and 52 a-52 gdepicted in FIGS. 6 and 7 overlaid in a single figure. As can be seen inFIG. 8, by propagating through the prism assembly 30 along the twodifferent optical paths, a pair of interfering coherent output beams isgenerated from the single incident beam (light ray 50 a/52 a). The pairof interfering coherent output beams reach the detector 36 and are usedto build up an interferogram by way of scanning of the optical pathdifference (as will be discussed with reference to FIG. 9). The outputbeams are separated by a distance, designated d in FIG. 8, which isreferred to as “lateral shear”, and is measured along a directionparallel to the edge joining surfaces 24 and 29. The pair of interferingcoherent beams is schematically represented by the parallel light rays50 g and 52 g, which are spaced apart by the distance d.

Parenthetically, when the prisms 12, 22 are right-angled prisms, theangle at which light rays enter the first prism 12 (via the surface 14)is the same as the angle at which the light rays exit the second prism22 (via the surface 24). However, as noted above, the entry and exitangles of light rays may not be identical in the case where the prisms12, 22 are non-right-angled prisms. Nevertheless, the two coherent beamsstill exit the prism assembly 30 along a parallel trajectory (i.e., thelight rays are spaced apart parallel rays) as long as the prisms aregeometrically similar, which means that the angle γ′ of exit of the twocoherent beam is the same.

The sets of coherent beams at the output of the prism assembly 30represent the various monochromatic components of the incident beam. Asshould be apparent, the results can be extrapolated for each light rayspanning a beam, and further extrapolated for other beams spanned bylight rays which may be parallel or non-parallel to the light rays ofother beams.

At the output of the prism assembly 30, the various monochromaticcomponents of an incident beam interfere according to phase differences.These monochromatic components are recombined at the detector 36, whereeach component contributes a different amount to the total signal outputby the detector 36. In general, the contribution is maximum if the phasedifference (at a given wavelength) between the components is an eveninteger multiple of π, and the contribution is minimum if the phasedifference between the components is an odd integer of π. The signalsoutput by the detector 36 can be stored as a function of the opticalpath difference (OPD) between various monochromatic components. In thecontext of the embodiments of the present disclosure, the OPD isgenerally defined as the difference between the first and second opticalpath lengths. Using the example illustrated in FIGS. 6-8, the detector36 output is stored as a function of the difference in the optical pathtraversed by the light rays 50 a-50 g and the light rays 52 a-52 g. TheOPD is typically scanned in order to build up an interferogram, andspectral analysis (e.g., Fourier Analysis via Fourier Transform) can beapplied to the interferogram to the determine the spectralcharacteristics of the source of light 34 as a function of wavenumber(inverse of wavelength).

The OPD is preferably scanned so as to cover a range of correspondingangles of incidence of light on the interferometer (optical device 10)such that the OPD varies as a function of the incident angle. Thevariability of the OPD as a function of incident angle is made possibleby the non-symmetry of the two prism 12, 22, which in the presentembodiment is effectuated by the presence of the offset amount 32.Therefore, it is critical to note that if no offset amount 32 werepresent, i.e., if the prism assembly was instead formed from twoidentical and symmetrically positioned prisms, the OPD would remainconstant and equal to zero during scanning (i.e., adjustment of theincident angle) and therefore would not vary as a function of theincident angle (measured between the light rays emitted by the source oflight 34 and the incident surface of the prism assembly). In otherwords, in order for the OPD to vary as a function of the incident anglein ways that are useful for the purposes of the present invention, theprisms 12, 22 should be mutually geometrically similar and shouldotherwise be symmetric about a plane of symmetry, except for the scalingand/or translating of one of the prisms with respect to the other of theprisms in the ways described in the present document.

The scanning of the OPD can be effectuated by using a scanningarrangement which adjusts the angle of incidence of incoming light raysfrom the source of light 34 relative to the incidence surface of theprism assembly 30, and the buildup of the interferogram and spectralanalysis may be performed by a processing system. FIG. 9 illustrates theoptical device 10 corresponding to the structure detailed with respectto FIGS. 6-8, combined with a scanning arrangement 46 and a processingunit 40, linked to the scanning arrangement 46 and the detector 36, toform an expanded optical device (referred to also as an optical system100). The scanning arrangement 46 can be implemented in various ways,including, for example, as a rotation and/or translation mechanism thattranslates either the source of light 34, or more preferably, rotatesthe prism assembly 30, about an axis of rotation that is parallel to theedges 15, 17, 25, 27, i.e., normal to the surfaces 19, 29 (normal to theplane of the paper), or jointly translates the prism assembly 30together with the detector 36 relative to the source of light 34. Insuch implementations, the rotation/translation mechanism preferablyincludes an electro-mechanical drive arrangement, such as amotor/actuator mechanically linked to the prism assembly 30 or thesource of light 34 via a rotatable rod to effectuate controlledrotation. When implemented as a rotational mechanism that rotates theprism assembly 30, the axis of rotation preferably passes through thebeamsplitter configuration 20 near the region of the beamsplitter wherethe beams intersect the beamsplitter configuration 20 (the region isnear the top if the beams enter near the top of the prism assembly 30,but is lower if the beams enter through the lower section of the prismassembly 30). This point is generally designated 48 in FIG. 9.

The scanning arrangement 46 may alternatively be implemented as ascanning mirror that deflects light rays from the source of light 34towards the prism assembly 30 over a range of prescribed incidentangles.

Note that the construction of the optical device 10, in particular theconstruction of the prism assembly 30, provides some advantage overother interferometer constructions. For example, the stability of theprism assembly 30 due to the solid construction from constituent prisms12, 22 that are optically cemented together (or mechanically joinedtogether), ensures that during movement of the prism assembly 30 orduring deployment of the optical device (for example as part of aplatform mounted spectral imager), all of the subcomponents of the prismassembly 30 move in unison, without any relative movement between thesubcomponents.

As the OPD is scanned by the scanning arrangement 46, the processingunit 40 stores the signals output by the detector 36 as a function ofthe optical path difference (OPD) traversed by the coherent beams in astorage medium, such as a memory 44 of the processing unit 40, to buildup an interferogram. A processor 42 of the processing unit 40 that islinked to the memory 44 applies spectral analysis algorithms, such asthe Fourier Transform, to the interferogram to the determine thespectral characteristics of the source of light 34 as a function ofwavenumber (inverse of wavelength). It is noted that the processing unit40 may include multiple processors 42 and storage media. The processor42 can be implemented as any number of computer processors including,but not limited to, a microprocessor, a microcontroller, an ASIC, and aDSP. Such processors include, or may be in communication with computerreadable media, which stores program code or instruction sets that, whenexecuted by the processor, cause the processor to perform actions. Typesof computer readable media include, but are not limited to, electronic,optical, magnetic, or other storage or transmission devices capable ofproviding a processor with computer readable instructions. As should beapparent, all of the components of the processing unit 40 are connectedor linked to each other (electronically) either directly or indirectly.

The processing unit 40 preferably provides control functionality forcontrolling the scanning arrangement 46 to operate in synchrony with thedetector 36. Generally speaking, the processor 42 can be configured toprovide control signals to the scanning arrangement 46 to actuate thescanning arrangement 46 to adjust the angle of incidence (e.g., viarotation of the prism assembly 30 or the source of light 34). In otherembodiments, a dedicated electronic control unit, separate from, butlinked to, the processing unit 40, may be used to provide the controlfunctionality. In yet other embodiments, the processing unit 40 mayinclude an additional dedicated processor, separate from the processor42, configured to provide control signals to the scanning arrangement46.

Referring again to FIGS. 6-8, it is noted that each of the coherentbeams generated inside the interferometer undergoes a single reflectionand a single transmission at the beamsplitter configuration 20. Thisensures that interfering rays reach the detector 36 with a highintensity modulation between in-phase and out-of-phase components, bycompensating for variability in the transmission and reflectioncoefficients of the beamsplitter configuration 20 and enables retainingof a maximum amount of spectral information in the signal. The followingparagraphs provide a general analysis of the intensity modulation forthe light rays (representative of the beams) that traverse the prismassembly 30 according to the illustrative example in FIGS. 6-8.

The amplitude A₁ of the emerging wavefront corresponding to the lightray 50 g can generally expressed as:A ₁ =r*t*Awhere r is the reflection coefficient for the amplitude of the electricfield of a plane wave at the surface of the beamsplitter configuration20, t is the transmission coefficient for the amplitude of the electricfield of a plane wave at the surface of the beamsplitter configuration20, and A is the amplitude of the wavefront incident to the beamsplitterconfiguration 20 (i.e., the wavefront corresponding to the light ray 50b).

Assuming that the angles of incidence to the surface of the beamsplitterconfiguration 20 in reflection and transmission are the same for theincident light ray 50 b and the incident light ray 52 b, the amplitudeA₂ of the emerging wavefront corresponding to the light ray 52 g cangenerally expressed as:A ₂ =r*t*A.

As should be apparent from the above, A₁=A₂. When these two wavefrontsare in-phase, the resulting light intensity on the detector 36 ismaximum, and can be expressed as:I _(max)=(A ₁ +A ₂)²=(2*r**t*A)²=4*r ² *t ² *A ².

When these two wavefronts are out-of-phase, the resulting lightintensity on the detector 36 is minimum, and can be expressed as:I _(min)=(A ₁-A ₂)²=0.

The intensity modulation M of an interferogram is expressed as:

$M = {2*\frac{I_{\max} - I_{\min}}{I_{\max} + I_{\min}}}$which by substituting the above expressions for I_(max) and I_(min)yield M=2.

As may be apparent from FIGS. 6-8, a proportion of the intensity of thelight ray 50 e is also transmitted by the beamsplitter configuration 20toward the first surface 14. Similarly, a proportion of the intensity ofthe light ray 52 e is reflected by the beamsplitter configuration 20toward the first surface 14 along a colinear trajectory to thetransmitted ray. By deploying an additional detector in association withthe first surface 14, approximately half of the light intensity lost bytransmission of the light ray 50 e and reflection of the light ray 52 ecan be gathered as interfering light rays by the additional detector andprovided to the processing unit 40 to generate an interferogram fromthese so-called “lost rays”, which are out-of-phase with thecorresponding light rays 50 e and 52 e. The additional interferogram maybe averaged, by the processing unit 40, with the interferogramcorresponding to the light rays 50 e and 52 e to improve the overallspectral results.

FIGS. 10 and 11 show the traversal of light rays from the source oflight 34 to a second detector 38 along respective third and fourthoptical paths (having respective third and fourth optical path lengths).

Looking first at FIG. 10, the light ray 50 a follows the same portion ofthe first optical path (FIG. 6) up to when the light ray 50 e reachesthe beamsplitter configuration 20. In contrast to the optical pathillustrated in FIG. 6, in the present figure a proportion of theintensity of the light ray 50 e is transmitted by the beamsplitterconfiguration 20, and is designated as light ray 50 h. The light ray 50h exits the first prism 12 via transmission by the first surface 14, andis designated as light ray 50 i, whereupon the light ray 50 i reachesthe second detector 38 that is associated with the first surface 14.When the light ray 50 h is incident to the surface 14 at an obliqueangle, the light ray 50 h is refracted upon exiting the prism 12 suchthat the light ray 50 i propagates at an angle of γ (relative to thenormal to the surface 14).

Referring now to FIG. 11, the light ray 52 a follows the same portion ofthe second optical path (FIG. 7) up to when the light ray 52 e reachesthe beamsplitter configuration 20. In contrast to the optical pathillustrated in FIG. 7, in the present figure a proportion of theintensity of the light ray 52 e is reflected by the beamsplitterconfiguration 20, and is designated as light ray 52 h. The light ray 52h, generally colinear to the light ray 50 h, exits the first prism 12via transmission by the first surface 14, and is designated as light ray52 i, whereupon the light ray 50 i reaches the second detector 38. Whenthe light ray 52 h is incident to the surface 14 at an oblique angle,the light ray 52 h is refracted upon exiting the prism 12 such that thelight ray 52 i propagates at an angle of γ (relative to the normal tothe surface 14).

It is noted that similar to the propagation from the source of light 34to the detector 36, a pair of coherent output beams (schematicallyrepresented by the light rays 50 i and 52 i) is generated from thesingle incident beam (light ray 50 a/52 a) due to the propagationthrough the prism assembly 30 along two different optical paths. Thispair of coherent output beams reaches the second detector 38, and areseparated by a lateral shear distance (not shown in the drawings).

Although not shown in the drawings, a lens arrangement may be deployedin the optical path between the surface 14 and the second detector 38 soas to focus the light rays exiting the first prism 12 (e.g., the lightrays 50 i and 52 i) onto the detector 36

It is noted that the light that follows the third optical path istransmitted by the beamsplitter configuration 20 twice, but is notreflected by the beamsplitter configuration 20. Conversely, the lightthat follows the fourth optical path is reflected by the beamsplitterconfiguration 20 twice, but is not transmitted by the beamsplitterconfiguration 20. The imbalance between reflection and transmission forthese two optical paths results in a smaller intensity modulation thanthe intensity modulation of light following the optical pathsillustrated in FIGS. 6-8.

Since the wavefront corresponding to the light ray 50 i undergoes twotransmissions by the beamsplitter configuration 20, the amplitude B₁ ofthe emerging wavefront can generally expressed as:B ₁ =t ² *A,and similarly, since the wavefront corresponding to the light ray 52 iundergoes two reflections by the beamsplitter configuration 20, theamplitude B₂ of the emerging wavefront can generally expressed as:B ₂ =r ² *A.

When these two wavefronts are in-phase, the resulting light intensity onthe detector 36 is maximum, and can be expressed as:I _(max)′=(B ₁ +B ₂)²=(r ² +t ²)² *A ².

When these two wavefronts are out-of-phase, the resulting lightintensity on the detector 36 is minimum, and can be expressed as:I _(min)′=(B ₁ −B ₂)²=(r ² −t ²)² *A ².

The intensity modulation M′ of the interferogram is expressed as:

$M^{\prime} = {{2*\frac{I_{\max}^{\prime} - I_{\min}^{\prime}}{I_{\max}^{\prime} + I_{\min}^{\prime}}} = {4\frac{r^{2}*t^{2}}{r^{4} + t^{4}}}}$

Assuming that the beamsplitter configuration 20 is not an ideal 50%-50%beamsplitter (i.e., that the proportion of light that is reflected bythe beamsplitter surface is not exactly equal to the proportion of lightthat is transmitted by the beamsplitter surface), the followinginequality is true:(r ² −t ²)²>0.

Expanding and simplifying the expression in parenthesis yields thefollowing inequality:

$\frac{r^{2}*t^{2}}{r^{4} + t^{4}} < \frac{1}{2}$which when substituted into the expression for M′ yields the followinginequality:

${M^{\prime} < {4*\frac{1}{2}}} = {2 = {M.}}$

As a result, for a non-ideal beamsplitter, the intensity modulation oflight following the optical paths illustrated in FIGS. 10 and 11 is lessthan the intensity modulation of light following the optical pathsillustrated in FIGS. 6-8. In general, the modulation is related to thedynamic range of the interferogram because the spectral information ofinterest is contained primarily in the relative amount of signalvariation with respect to its average. The relative signal variation ismaximized when the minimum light intensity is identically zero (as inthe case that is described with reference to FIGS. 6-8). When minimumlight intensity is not identically zero (as in the case that isdescribed with reference to FIGS. 10 and 11), the intensity modulationis reduced, resulting in a loss of some of the spectral informationcarried in the signal variations of the interferogram.

As previously mentioned, the use of the second detector 38 enablesgathering of “lost rays” to produce an additional interferogram that canbe averaged with the interferogram corresponding to the light rays 50 eand 52 e. The ability to capture these “lost rays” can improve theoverall sensitivity of the optical device 10. In contrast, in mostconventional interferometers the “lost rays” are typically directed backtoward the source and cannot be captured by an additional detector. Itis noted, however, that instead of using the second detector 38 tocapture “lost rays”, an absorber material may be positioned in place ofthe second detector 38 to prevent ghost rays, due to unwantedreflections, from reaching the primary detector 36.

In addition, the second optical channel through which the “lost rays”propagate can also be exploited to support high-accuracy radiometricand/or wavelength calibration, for example by deploying one or morespecialized sources (e.g., monochromatic or wideband light sources) atthe exit side of the prism assembly 30 (i.e., at or near the surface24).

As previously discussed, the formation of the interferometric opticaldevice from two identical triangular prisms that are shifted, one withrespect to the other, by an offset amount, promotes a relationshipbetween the OPD and the angle of incidence of light (from the source oflight 34) to the entrance surface of the prism assembly. It isparticularly desirable that this relationship be a linearrelationship—or as close to a linear relationship as possible—such thatthe OPD varies as a linear function (or nearly linear function) of theincident angle. In the case of near linearity, the maximum OPD value,which in interferometry determines the achievable spectral resolution ofthe optical system, is achieved at the largest angle of incidence asmeasured with respect to the normal to the first surface. In order toachieve this linear or near linear functional relationship between OPDand incident angle, embodiments are contemplated in which one of theprisms is a scaled and shifted version of the other prism. FIGS. 12-14illustrate various views of an optical device according to suchembodiments.

Referring first to FIG. 12, there is shown a schematic plan view of anoptical device formed from two geometrically similar prisms 12, 22having a beamsplitter configuration 20 deployed therebetween. Thestructure of the optical device of FIG. 12 is nearly identical to thestructure of the optical device illustrated in FIGS. 1-11 except that inthe present embodiment the second prism 22 is a scaled-down and mirroredversion of the first prism 12. Here, the front surface 29 (and itsopposing rear surface) of the second prism 22 is uniformly scaled-down(in two dimensions) relative to the front surface 19 of the first prism12, and the surfaces 24, 26, 28 are scaled-down (preferably in onedimension) relative to the corresponding surfaces 14, 16, 18. Inparticular, the surfaces 24, 26, 28 are preferably scaled only along thedimension of the respective edges formed between the respective surfaces24, 26, 28 and the front surface 29 such that the prisms 12 and 22 havethe same thickness (i.e., such that the surfaces 19 and 29 are coplanar,and the two surfaces opposing the surfaces 19 and 29 are coplanar).

Due to the property of geometric similarity, the two prisms 12, 22 haveidentical internal angles and the length of each of the three mainsurfaces of one of the prisms is a scalar multiple of the length of thecorresponding main surface of the other prism. In the presentembodiment, the length of the third surface 18 (measured in thedimension spanned by the edge formed by the surfaces 18 and 19) isarbitrarily labeled a, and the length of the third surface 28 (measuredin the dimension spanned by the edge formed by the surfaces 28 and 29)is arbitrarily labeled a′, where a is different than a′.

FIG. 13 more clearly shows the interface region 31 of the optical deviceof FIG. 12. Unlike the interface region of the optical device of FIGS.1-11, the surfaces 16, 26 of the prism assembly of the presentembodiment mutually overlap such that the interface region 31 extendsalong unequal portions (unequal majority portions in the illustratedexample) of the second surfaces 16, 26 along the dimension of the edgethat joins together the surface 16 and the surface 19 (and equivalentlythe edge that joins together the surface 26 and the surface 29).Analogously, the second surfaces 16, 26 mutually overlap such that aminority portion of the surface 16 extends beyond the surface 26 by afirst given offset amount 33 and a minority portion of the surface 26extends beyond the surface 16 by a second given offset amount 32, wherethe first and second given offset amounts are unequal and are measuredin the dimension of the edge that joins together the surface 16 and thesurface 19 (and equivalently the edge that joins together the surface 26and the surface 29). In the particular illustrative example of FIG. 13,the amount by which the surface 16 extends beyond the surface 26 isgreater than the amount by which the surface 26 extends beyond thesurface 16. By further analogy, the second surfaces 16, 26 mutuallyoverlap such that the edge 25 of the second prism 22 extends beyond theedge 15 of the first prism 12 by the second given offset amount 32(measured along the dimension of the edge that joins together thesurface 16 and the surface 19), and the edge 17 of the first prism 12extends beyond the edge 27 of the second prism 22 by the first givenoffset amount 33 (measured along the dimension of the edge that joinstogether the surface 16 and the surface 19).

FIG. 14 shows the optical device deployed in an optical path between thesource of light 34 and the detector 36, and in particular shows thepropagation of a beam emitted by the source of light 34 to the detector36 along first and second optical paths (having corresponding respectivefirst and second optical path lengths) through the prism assembly formedfrom the prisms 12, 22.

Along the first optical path, the light beam, represented schematicallyin FIG. 14 as a sample light ray 54 a, is incident to the first surface14 at an incident angle of γ (where the incident angle is measuredrelative to the normal to the surfaced 14, shown by the dotted linecrossing the surface 14). The incident light ray 54 a is transmitted bythe first surface 14. The transmitted light ray, designated 54 b, isrefracted (for γ≠0) upon entering the first prism 12 such that itpropagates at an angle of ft (measured relative to the normal to thesurfaced 14).

The transmitted light ray 54 b impinges on the beamsplitterconfiguration 20 where a proportion of the intensity of the light ray 54b is transmitted by the beamsplitter configuration 20, and is designatedas light ray 54 c. The transmitted light ray 54 c impinges on the firstsurface 24 of the second prism 22 at an angle greater than the criticalangle such that it is totally internally reflected as light ray 54 d.The light ray 54 d propagates toward the third surface 28 and impingeson the third surface 28 at an angle greater than the critical angle suchthat it is totally internally reflected as light ray 54 e.

The light ray 54 e propagates toward the beamsplitter configuration 20where a proportion of the intensity of the light ray 54 e is reflectedby the beamsplitter configuration 20, and is designated as light ray 54f. The light ray 54 f exits the second prism 22 via transmission by thefirst surface 24. The transmitted light ray is designated as 54 g. Whenthe light ray 54 f is incident to the surface 24 at an oblique angle,the light ray 54 f is refracted upon exiting the prism 22 such that thelight ray 54 g propagates at an angle of γ (relative to the normal tothe surface 24), whereupon the transmitted light ray 54 g reaches thedetector 36.

Along the second optical path, the light beam, represented schematicallyin FIG. 14 as a sample light ray 56 a (which is the same as the lightray 54 a), is incident to the first surface 14 at an incident angle ofγ, and is transmitted by the first surface 14. The transmitted lightray, designated 56 b (which is the same as the light ray 54 b), isrefracted (for γ≠0) upon entering the first prism 12 such that itpropagates at an angle of β.

The transmitted light ray 56 b impinges on the beamsplitterconfiguration 20 where a proportion of the intensity of the light ray 56b is reflected by the beamsplitter configuration 20, and is designatedas light ray 56 c. The reflected light ray 56 c impinges on the firstsurface 14 of the first prism 12 at an angle greater than the criticalangle such that it is totally internally reflected as light ray 56 d.The light ray 56 d propagates toward the third surface 18 and impingeson the third surface 28 at an angle greater than the critical angle suchthat it is totally internally reflected as light ray 56 e.

The light ray 56 e propagates toward the beamsplitter configuration 20where a proportion of the intensity of the light ray 56 e is transmittedby the beamsplitter configuration 20, and is designated as light ray 56f. The light ray 56 f exits the second prism 22 via transmission by thefirst surface 24. The transmitted light ray is designated as 56 g. Whenthe light ray 56 f is incident to the surface 24 at an oblique angle,the light ray 56 f is refracted upon exiting the prism 22 such that thelight ray 56 g propagates at an angle of γ (relative to the normal tothe surface 24), whereupon the transmitted light ray 56 g reaches thedetector 36.

As should be apparent from the description of the traversal of lightrays corresponding to FIG. 14, light rays traversing the optical paththrough the prism assembly 30 enter the first prism 12 and exit thesecond prism 22 at the same angle γ.

It is noted that the same options discussed above, pertaining to the useof a specular or an ASR coating instead of, or in combination with,construction of the prisms 12, 22 from an appropriately high indexmaterial, are applicable here. It is further noted the order ofreflection from the surfaces 24, 28 and the surfaces 14, 18 may bereversed, similar to as previously discussed, by adjusting the positionof the source of light 34 such that the light rays 54 b, 56 b impinge onthe beamsplitter configuration 20 at a region closer to the upperportion of the interface region 31. Finally, it should be apparent thatthe optical device of the present embodiment (FIGS. 12-14) can also beused in combination with a second detector 38 (associated with the firstsurface 14) and/or as part of the optical system 100 illustrated in FIG.9.

Although the configuration illustrated in FIGS. 12-14 shows the smallerprism placed higher than the larger prism, other configurations arepossible in which the larger prism is placed higher than the smallerprism.

Parenthetically, in all of the examples described and illustrated inthis document, the corners relating to the apex angle α and to theopposite corner near the edges 15, 25, can be absent, meaning that theprisms 12, 22 can be cut (removing at least the portions of the prism12/22 which extends beyond the prism 22/12), as long as this absencedoes not interfere with the path of the beams inside the prisms. FIG. 19illustrates an example of such an optical device having cut-off corners,based on the optical device of FIG. 12. Here, the corners relating tothe apex angle α of the prisms 12 and 22 are cut-off (by a single cut),resulting in an additional surface 11 a of the prism 12 that extendsbetween the surfaces 12 and 16, normal to the plane of the beamsplitterconfiguration 20, and an additional surface 21 of the prism 22 thatextends between the surfaces 24 and 26, normal to the plane of thebeamsplitter configuration 20. The non-apex corners of the prisms 12 and22 that are close to the beamsplitter configuration 20 are also cut-off(by a single cut), resulting in an additional surface 11 b of the prism12 that extends between the surfaces 16 and 18, normal to the plane ofthe beamsplitter configuration 20, and an additional surface 21 b of theprism 22 that extends between the surfaces 26 and 28, normal to theplane of the beamsplitter configuration 20. As mentioned, the prisms 12and 22 may be cut so long as the removal of the cut-off portions doesnot interfere with the path of beams inside the prism assembly 30.Specifically, the portions of the surfaces 14, 18, 24 and 28 removed bythe cutting should not include the regions of those surfaces whichreflect light during propagation through the prism assembly 30. AlthoughFIG. 19 illustrates the optical device of FIG. 12 with cut-off corners,it should be clear that similar corner cut-off principles can be appliedto the various other optical devices described and illustrated in thisdocument. It is also noted that the prisms 12 and 22 may be cut prior toformation of the unitary prism assembly 30, or may be cut after theunitary prism assembly 30 has been formed.

The following paragraphs describe design considerations of the opticaldevice of the various embodiments of the present disclosure which enableachieving an OPD that is a function of the sine of the incident angle γ,and in particular is proportional to sin γ. As a result, in theseconfigurations the OPD will be equal to 0 when γ=0. On this basis, it istherefore also possible to identify the condition needed to cause theOPD to be equal to zero for an incident angle different from zero.

Assuming that the prisms 12, 22 are constructed from a material having arefractive index of η, and the prism assembly is deployed in a mediumhaving refractive index of 1 (e.g., air), the relationship between theincident angle γ and the refracted angle β is given by:

$\eta = \frac{\sin\mspace{11mu}\gamma}{\sin\mspace{11mu}\beta}$

Generally speaking, there are two contributions to the OPD for any pairof coherent beams that reach the detector 36 along two different opticalpaths. The first contribution can be attributed to the traversal of thetwo beams through the prism assembly, and the second contribution isattributed to the “lateral shear” between the two beams. As previouslymentioned, the “lateral shear” is generally defined as the distance(measured parallel to the direction of the edge joining planes 24 and29) between the two beams at the exit of the prism assembly (e.g., thedistance between the spaced apart parallel rays 50 g and 52 g in FIGS.6-8). In drawings (FIGS. 8 and 14), the lateral shear is designated asd. Parenthetically, lateral shear is also present in embodiments inwhich the prisms 12, 22 are non-right-angled prisms.

The OPD contribution from traversing the prism assembly is denoted asOPD_(P), and is expressed as:

${OPD}_{P} = {2*\eta*\frac{{\left( {a - a^{\prime}} \right)*\cos\; 2\alpha} - {b*\sin\mspace{11mu}\alpha}}{\cos\mspace{11mu}\beta}}$where b is the given offset amount 32.

The OPD contribution from the lateral shear d is denoted as OPD_(S), andis expressed as:OPD_(S) =−d*sin γ

It turns out that the lateral shear d does not depend on the incidentangle γ, and only depends on the geometry and the offset amount of theprisms 12, 22. Specifically, the lateral shear d can be expressed as:d=2*{b*cos α+(a−a′)*sin 2α}

The total OPD, denoted as OPD_(T), is given by the sum of the two OPDcontributions, i.e., OPD_(T) is expressed as:OPD_(T)=OPD_(P)+OPD_(S)

For the optical device of FIGS. 1-11, the two prisms 12 and 22 are ofthe same size, and therefore a=a′. Thus, the above expression for thelateral shear can be simplified to:d=2*b*cos α.

Accordingly, for the particular case of two identically sized prismshaving an offset amount 32, the lateral shear is a function of theoffset amount 32 (given as b), and the apex angle α of the constituentprisms 12, 22. Thus, the OPD contribution from the lateral shear can beexpressed as:OPD_(S)=−2*b*cos α*sin γ

In addition, the above expression for the OPD contribution fromtraversing the prism assembly 30 of FIGS. 1-11 can be simplified (bysetting a=a′) to:

${OPD}_{P} = {{{- 2}*\eta*b*\frac{\sin\mspace{11mu}\alpha}{\cos\mspace{11mu}\beta}} = {{- 2}*\eta*b*\sin\mspace{11mu}{\alpha/{\cos\left\lbrack {{asin}\left( \frac{\sin\mspace{11mu}\alpha}{\eta} \right)} \right\rbrack}}}}$

Thus, the total OPD, given by the sum of OPD and OPD_(S), for theoptical device of FIGS. 1-11 can be expressed as:

${OPD}_{T} = {{{- 2}*b*\eta*\frac{\sin\mspace{11mu}\alpha}{\cos\left\lbrack {{asin}\left( \frac{\sin\mspace{11mu}\gamma}{\eta} \right)} \right\rbrack}} - {2*b*\cos\mspace{11mu}\alpha*\sin\mspace{11mu}\gamma}}$which is a function of sin γ. Here, the OPD is obviously ≠0 when γ=0,because then only the second term of the equation is equal to zero. Inaddition, in the previous equation, the OPD_(T) may in general not beequal to 0 for any value of γ. In fact, for example for OPD_(T) to bezero, the following relationship should hold:

${\sin\mspace{11mu}\gamma*{\cos\left\lbrack {{asin}\left( \frac{\sin\mspace{11mu}\gamma}{\eta} \right)} \right\rbrack}} = {{- \eta}\;\tan\mspace{11mu}\alpha}$

The right-hand side of the above expression is negative, so the equalitycan be satisfied only if γ is negative (since −90°<γ<90°). However,although for 0°>γ>−90° the left-hand side of the above expression isnegative, it is always larger than −0.826, while for a=22.5° and η=2.4(e.g., for ZnSe), the right side of the equation is negative and isequal to approximately −0.9941. As a result, in this case, the OPD_(T)never becomes 0 for any incident angle γ. The same situation can beproved to hold in general also if the two prisms are not the same sizebut the offset amount is zero.

For the optical device of FIGS. 12-14, the simplified expressions forOPD and OPD_(S) do not hold, since a≠a′. In this case, it turns out thatin general there is a set of geometric parameters of the prisms 12, 22and the offset amount between them for which OPD is equal to 0 withoutnulling OPD_(S). It follows that in this case OPD_(T) is equal toOPD_(S), and therefore is proportional to sin γ. This case is preferablewhen double sided and symmetric interferograms are desired, where thetotal OPD can take positive and negative values and takes a value ofzero in the central field of view angle of the optical system.

To find the proper conditions for this to happen, the equation for OPDis set to 0, resulting in the following expression:

$b = \frac{\left( {a - a^{\prime}} \right)*\cos\mspace{11mu} 2\alpha}{\sin\mspace{11mu}\alpha}$

By substituting the expression for b (the second given offset amount 32)into the expression for the lateral shear d, and using appropriatetrigonometric identities, the expression for lateral shear d can bewritten as:

$d = {2*\left\{ {{\frac{\left( {a - a^{\prime}} \right)*\cos\mspace{11mu} 2\alpha}{\sin\mspace{11mu}\alpha}*\cos\mspace{11mu}\alpha} + {\left( {a - a^{\prime}} \right)*\sin\mspace{11mu} 2\alpha}} \right\}}$which can be simplified to:

$d = {2*\left( {a - a^{\prime}} \right)*\left( {{\sin\mspace{11mu} 2\alpha} + \frac{\cos\mspace{11mu} 2\alpha*\cos\mspace{11mu}\alpha}{\sin\mspace{11mu}\alpha}} \right)}$

Using the double angle identities for sine and cosine, the expressionfor the lateral shear d can ultimately be reduced to:d=2*(a−α′)*cot αAs should be apparent, the lateral shear d in these expressions could beidentically equal to 0 (meaning that the light rays 54 g and 56 g arenot only parallel, but are also colinear) in two cases: 1) when theprisms 12, 22 are identical in size (i.e., a=a′), and/or 2) when α is90°. However, this is not the case by definition, because the prisms 12,22 in FIGS. 12-14 are of different size (i.e., a≠a′), and the angle α isthe apex angle and is by definition less than 90°.

Accordingly, in order to achieve a double sided interferogram (wherenegative OPD values are included in the interferogram) or at least aninterferogram in which the OPD is equal to 0 for some incident angle γ,the two prisms 12, 22 are of unequal size and translated one withrespect to the other whereby none of the edges 15, 17 of the first prism12 are aligned with the corresponding edges 25, 27 of the second prism22. By appropriate choice of the values of b, a and a′ (according to thepreviously defined relationship between b and a, a′, or approximatelyaccording to that relationship), an OPD value of 0 is achievable forγ=0. More precisely, in conclusion, if

${b = \frac{\left( {a - a^{\prime}} \right)*\cos\mspace{11mu} 2\alpha}{\sin\mspace{11mu}\alpha}},$or equivalently, if the ratio

${\frac{b}{a - a^{\prime}} = {\cos\mspace{11mu} 2{\alpha/\sin}\mspace{11mu}\alpha}},$then,OPD_(T)=OPD=−d*sin γ=−2*(a−a′)*cot α*sin γ.

This expression of OPD_(T), a-a′ being different than 0, is zero onlyfor γ=0 and takes positive and negative values for γ varying around 0.OPD_(T) can be made to take the zero value for different values of γ, byslightly varying the ratio of

$\frac{b}{a - a^{\prime}}$above.

It is noted that spectroscopic applications often rely on the use ofdouble side interferograms because the full radiation intensityinformation is carried in the value of the interferogram at OPD=0.However, some spectral information is still available even when the fullradiation intensity information is absent. Accordingly, there ispotential value in modifying the optical device of FIGS. 12-14 to assumea configuration in which the prisms 12, 22 are either the same size andnot translated one with respect to the other, or are translated and notthe same size, such that an OPD value of 0 is not achievable. It isreiterated here that the case of two constituent prisms of the same sizeand no translation does not give rise to any OPD for any angle ofincidence.

By way of illustration of one such particular configuration of theprisms 12, 22, FIGS. 15-17 show an optical device similar to the opticaldevice described with respect to FIGS. 12-14, but in which the prisms12, 22 are not translated one with respect to the other. Specifically,the interface region 31 extends along the entirety of the length(measured in the dimension of the edge that joins together the surface16 and the surface 19) of one of the surfaces 16, 26 (the surface 26 inthe illustrative example), and extends along the majority of the lengthof the other of the surfaces 16, 26 (the surface 16 in the illustrativeexample). Analogously, the second surfaces 16, 26 mutually overlap suchthat a minority portion of the surface 16 extends beyond the surface 26by a given offset amount 32 in the dimension of the edge that joinstogether the surface 16 and the surface 19, but the surface 26 does notextend beyond the surface 16.

FIGS. 15 and 16 show a configuration in which the second surfaces 16, 26mutually overlap such that the edge 17 of the first prism 12 extendsbeyond the edge 27 of the second prism 22 by the given offset amount 32(measured along the dimension of the edge that joins together thesurface 16 and the surface 19), but the edges 15 and 25 are mutuallyaligned. FIG. 17 illustrates a configuration similar to theconfiguration of FIGS. 15 and 16, but with the translation in theopposite direction. Specifically, in the configuration illustrated inFIG. 17, the second surfaces 16, 26 mutually overlap such that the edge15 of the first prism 12 extends beyond the edge 25 of the second prism22 by the given offset amount 32 (measured along the dimension of theedge that joins together the surface 16 and the surface 19), but theedges 17 and 27 are mutually aligned.

It is noted that each of the configurations of the optical devicesillustrated in FIGS. 1-17 has a corresponding symmetric configuration inwhich the source of light 34 and the detector 36 positions are swappedsuch that the surface 24 is associated with the source of light 34 (andthe second detector 38), and the surface 14 is associated with thedetector 14.

As should be apparent, the various configurations of the prism assembly30 described herein are all variants of each other, and oneconfiguration can be achieved from another configuration by makingappropriate changes to some of the parameters of the constituent prismsand the size of the interface region. For example, the configuration ofthe prism assembly 30 illustrated in FIG. 12 can be achieved from theconfiguration of the prism assembly 30 illustrated in FIG. 3 by makingthe lengths of the surfaces 18 and 28 unequal (i.e., a≠a′). Similarly,the configuration of the prism assembly 30 illustrated in FIG. 3 can beachieved from the configuration of the prism assembly 30 illustrated inFIG. 12 by setting the lengths of the surfaces 18 and 28 to be equal toeach other (i.e., a=a′). Similarly, the configuration of the prismassembly 30 illustrated in FIG. 15 can be achieved from theconfiguration of the prism assembly 30 illustrated in FIG. 3 by makingthe lengths of the surfaces 18 and 28 unequal (i.e., a≠a′) andappropriately adjusting the size of the interface region.

As discussed throughout the present document, some of the drawings,notably FIGS. 6-8, 10, 11 and 14, illustrate schematic representationsof light propagation through the prism assembly 30 by way of light raytracing. Although the light rays have been illustrated in an effort toaccurately show angles of incidence, reflection, and refractionassociated with the light rays, it should be clear that these schematicrepresentations are intended to help illustrate how the beamsplitterconfiguration 20 and the prisms 12, 22 deflect incident lightoriginating from a source, and that the angles of incidence, reflection,and refraction gleaned from the drawings may not be precise. One ofordinary skill in the art will appreciate that the light propagatingthrough the prism assembly 30 will undergo refraction and reflection atangles from the various prism surfaces and the beamsplitterconfiguration in accordance with the underlying physical principles ofrefraction and reflection (e.g., total internal reflection, beamsplitterreflection, etc.).

The embodiments of the present disclosure have thus far been describedwith consideration of parallel light rays incident on the prism assembly30 which lay in a plane that is parallel to the planar surface 19 (andthe surface 29). If the detector 36 is a point detector or a multipleelement linear detector lying also on the plane of the paper, all of thespectral information can be gathered by scanning the γ angles (in caseof a point detector), or by storing the signals from all the detectorelements (in the case of the line detector), by imaging these parallelrays on the detector(s) through a lens or a set of lenses appropriatelyfocusing the incoming rays from infinity. However, if the detector 36 isa two-dimensional multiple element detector with a detector surfaceperpendicular to the plane of the paper, with first sets of detectorelement lines lying parallel to the plane of the paper, the orthogonaldetector element lines perpendicular to the first sets of detectorelement lines and having elements lying outside the plane of the paper,the elements of the orthogonal detector element lines will receive setsof parallel skew rays through the focusing lens system. These parallelskew rays travel in directions which are not parallel to the plane ofthe paper. It turns out that the component of a skew ray parallel to theplane of the paper propagates through the interferometer (the prismassembly 30) and contributes to the signal of the detector element ontowhich the ray is focused in the same way as described in the abovetreatment according to the appropriate projected γ angle. Especially inthe cases analyzed above of OPD_(T) going through 0 at γ=0 or at γ closeto 0, the OPD_(T) is a substantially fast varying function of γ (firstorder in γ). In contrast, the component of the skew ray which isperpendicular to the plane of the paper is expected to contribute a muchslower variation of OPD_(T) with the γ′ angle, defined as the projectedangle of the skew ray with respect to a direction perpendicular to theplane of the paper. The result of this fact is that the detectorelements of a two-dimensional detector will carry most of the spectralinformation in the direction parallel to the plane of the paper, andalmost no spectral information in a direction perpendicular to the planeof the paper (while all of the detector elements carry equally thespatial information from the different directions of the incoming rays).

It is noted that in the previously described embodiments, for each ofthe surfaces 14 and 24 only a specific region of the surface reflectslight during propagation through the prism assembly 30, and only aspecific region of the surface couples light into and out of the prismassembly 30. In general, the light coupling regions and light reflectingregions of the surfaces 14 and 24 are non-overlapping, such that theregions of the surfaces 14 and 24 at which light respectively enters andexits the prism assembly 30 are non-overlapping with the regions of thesurfaces 14 and 24 at which propagating light undergoes reflection(either by total internal reflection from the surfaces 14, 24 or via anASR or specularly reflecting coating applied to the surfaces 14, 24).Furthermore, for each of the surfaces 18 and 28, only a specific regionof the surface reflects light (either by total internal reflection fromthe surfaces 18, 28 or via an ASR or specularly reflecting coatingapplied to the surfaces 18, 28) during propagation through the prismassembly 30.

Embodiments are contemplated herein in which the non-light reflectingregions of the surfaces 14, 18, 24, 28 are replaced with air, and thelight reflecting regions are replaced with reflective surfaces. Anexample of an interferometer configuration based on the configurationillustrated in FIG. 14 is depicted in FIG. 18. The interferometer iscomposed of two mirror assemblies 60 and 70 and a beamsplitterconfiguration 20. Each of the mirror assemblies 60, 70 has acorresponding pair of generally planar reflective surfaces that form aright-angle (although other embodiments are considered fornon-right-angled mirror assemblies). Specifically, the mirror assembly60 includes a pair of reflective surfaces 62 and 64, and the mirrorassembly 70 includes a pair of reflective surfaces 72 and 74. The dashedlines in FIG. 18 demarcate the extensions of the planes of thereflective surfaces 62, 64, 72, 74 and the beamsplitter configuration 20(i.e., the regions at which light does not undergo any reflections).

In general, the size of, and the positional relations between, thereflective surfaces 62, 64, 72, 74 and the beamsplitter configuration 20is the same as the light reflecting regions and the used portion of thebeamsplitter configuration 20 of FIG. 14, except that in the presentembodiment the solid material of the prisms is removed and replaced withair to form an “air prism”. Specifically, the light reflecting regionsof the respective surfaces 14, 18, 24, 28 of the prism assembly 30 ofFIG. 14 are replaced by the reflective surfaces 62, 64, 72, 74 in thepresent embodiment. In addition, the light coupling regions of thesurfaces 14, 24 and the non-light reflecting regions of the surfaces 18,28 of the prism assembly 30 of FIG. 14 are replaced with air in thepresent embodiment.

The following paragraphs further describe the positional relationsbetween the surfaces 62, 64, 72, 74 and the beamsplitter configuration20 in the context of FIG. 18. Generally speaking, the mirror assemblies60, 70 and the beamsplitter configuration 20 are deployed such that theplanes of the reflective surfaces 62, 64 and the beamsplitterconfiguration 20 intersect to form a first prismatic structure (“airprism”) having a triangular shape in the plane of the paper. The planeof the reflective surface 62 and the plane of the beamsplitterconfiguration 20 intersect to form the apex angle of the triangular “airprism”. The planes of the reflective surfaces 72, 74 and thebeamsplitter configuration 20 intersect to form a second prismaticstructure (“air prism”) having a triangular shape in the plane of thepaper. The plane of the reflective surface 72 and the plane of thebeamsplitter configuration 20 intersect to form the apex angle of thetriangular “air prism”.

The triangles formed by the aforementioned planar intersections areoffset one with respect to the other and scaled one with respect to theother (just as in the configuration described with respect to FIG. 14).A point on the line of intersection between the plane of thebeamsplitter configuration 20 and the plane of the reflective surface 74extends beyond a colinear point on the line of intersection between theplane of the beamsplitter configuration 20 and the plane of thereflective surface 64 by a first given offset amount. Optionally, or inaddition, a point on the line of intersection between the plane of thebeamsplitter configuration 20 and the plane of the reflective surface 62extends beyond a colinear point on the line of intersection between theplane of the beamsplitter configuration 20 and the plane of thereflective surface 72 by a second given offset amount (that may be thesame as or different from the first given offset amount).

Alternatively, a point on the line of intersection between the plane ofthe beamsplitter configuration 20 and the plane of the reflectivesurface 64 extends beyond a colinear point on the line of intersectionbetween the plane of the beamsplitter configuration 20 and the plane ofthe reflective surface 74 by a first given offset amount. Optionally, orin addition, a point on the line of intersection between the plane ofthe beamsplitter configuration 20 and the plane of the reflectivesurface 72 extends beyond a colinear point on the line of intersectionbetween the plane of the beamsplitter configuration 20 and the plane ofthe reflective surface 62 by a second given offset amount (that may bethe same as or different from the first given offset amount).

It is noted that incident light to the configuration illustrated in FIG.18 follows a light propagation path similar to as described withreference to FIG. 14, however, since the mirror assemblies 60, 70 andthe beamsplitter configuration 20 are deployed in air (refractive indexof 1), incident light does not undergo refraction upon entering orexiting the “air prism”. As such, the optical paths traversed by anincident beam from the source of light to the detector (and optionallythe second detector) are equivalent to the respective geometrical paths(since the optical path is generally defined as the geometrical pathmultiplied by the refractive index).

As should be apparent to one of ordinary skill in the art, thereplacement of the light reflecting regions with reflective surfaces,and the replacement of the non-light reflecting regions with air, canequally be applied to other prism assembly 30 configurations describedherein, for example the configurations described with reference to FIGS.3, 15 and 17. All the equations describing the behavior of the total OPDversus incidence angle of the incoming rays will hold by setting theparameter η equal to 1.

It is noted that one advantage of the aforementioned “air prism”embodiments is that the air prisms require a relatively small amount ofsolid material, and are therefore cheaper to manufacture as compared totheir solid material prism counterparts.

It is noted herein, and with reference to the ray traversal diagrams(e.g., FIGS. 6-8, 10, 11 and 14), that the incoming light rays 50 a or54 a are representative of a respective parallel bundle of rays whichform the respective plane wavefront. Each of these bundles has a crosssection defined by collecting optics of the system in which theinterferometer (optical device 10) is operative. The region of firstsurface 14 through which the bundles enter the interferometer fromdifferent directions, and which is the intersection of this surface 14with the various bundles' cross sections, is arbitrary, as long as thevarious reflections and beamsplitter traversals take place according tothe explanations above. It has become apparent to the inventors thatthere is a preferred region of entrance which can be used to minimizethe size of the interferometer, at equal beam cross section and range ofentrance angles, so as to provide a reduced overall form factor of theoptical device. This preferred region is the region opposite to theupper corner of the prism 22 (the intersection between surfaces 24 and28). This region is preferred because in the configurations describedherein, the largest portion of the prism 22 on the side of the smallerapex angle (the intersection between surfaces 24 and 26) can be removed,resulting in a smaller interferometer in terms of volume and weight. Forbundles entering the prism 12 in the preferred region, and normal to thefirst surface 14, the light rays which compose the bundles aretransmitted by the beamsplitter configuration 20. For each of thetransmitted rays, a first portion of the transmitted ray impinges on thesurface 24 of the prism 22, and a second portion of the transmitted rayimpinges on the surface 28 of the prism 22.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

As used herein, the singular form, “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration”. Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

To the extent that the appended claims have been drafted withoutmultiple dependencies, this has been done only to accommodate formalrequirements in jurisdictions which do not allow such multipledependencies. It should be noted that all possible combinations offeatures which would be implied by rendering the claims multiplydependent are explicitly envisaged and should be considered part of theinvention.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

What is claimed is:
 1. An optical device comprising: a prism assemblyincluding: a first prism comprising a light-transmitting material havinga plurality of surfaces including at least a first surface associatedwith a source of light and a second surface oblique to the firstsurface, and a second prism comprising a light-transmitting materialhaving a plurality of surfaces including at least a first surfaceassociated with a detector and a second surface oblique to the firstsurface of the second prism, wherein the second surface of the firstprism is in overlapping relation with the second surface of the secondprism to define an interface region of a given length that partiallyextends along at least one of the second surface of the first prism orthe second surface of the second prism, and wherein the first and secondprisms are optically attached at the interface region; and abeamsplitter configuration overlying the interface region, wherein anincoming light beam emitted by the source of light is transmitted by thebeamsplitter configuration and is subsequently reflected by thebeamsplitter configuration so as to propagate through the prism assemblyalong a first optical path to the detector, and wherein the incominglight beam is reflected by the beamsplitter configuration and issubsequently transmitted by the beamsplitter configuration so as topropagate through the prism assembly along a second optical path to thedetector, such that the incoming light beam reaches the detector as twocoherent light beams, and wherein the plurality of surfaces of the firstprism further includes a third surface, and wherein the plurality ofsurfaces of the second prism further includes a third surface, andwherein light beams that propagate from the source of light to thedetector along the first optical path are reflected once from each ofthe first and third surfaces of the second prism, and wherein lightbeams that propagate from the source of light to the detector along thesecond optical path are reflected once from each of the first and thirdsurfaces of the first prism.
 2. The optical device of claim 1, wherein adifference between a length of the first and second optical paths variesas a function of an angle of incidence of the incoming light beam. 3.The optical device of claim 1, wherein the source of light is a remotescene that emits radiation.
 4. The optical device of claim 1, furthercomprising: a detector arrangement corresponding to the detectorassociated with the first surface of the second prism.
 5. The opticaldevice of claim 1, further comprising: a scanning arrangement configuredto change an angle of incidence of light beams, emitted by the source oflight, on the first surface of the first prism.
 6. The optical device ofclaim 1, wherein at least some of the reflections of the light beamsfrom the first and third surfaces of the first or second prism arereflections by total internal reflection.
 7. The optical device of claim1, wherein the light-transmitting material of the first and secondprisms have a refractive index greater than a refractive index of amedium in which the prism assembly is deployed so as to define acritical angle such that light beams that propagate along the first andsecond optical paths that are incident on the first and third surfacesof the first and second prisms at angles greater than the critical angleare reflected from the first and third surfaces of the first and secondprisms by total internal reflection.
 8. The optical device of claim 1,wherein the first surface of the first prism is further associated witha second detector, and wherein light beams emitted by the source oflight propagate through the first and second prisms along a thirdoptical path and a fourth optical path so as to reach the seconddetector as two coherent light beams, and wherein light beams thatpropagate from the source of light to the second detector along thethird optical path are reflected from the beamsplitter configurationexactly twice and are not transmitted by the beamsplitter configuration,and wherein light beams that propagate from the source of light to thesecond detector along the fourth optical path are transmitted by thebeamsplitter configuration exactly twice and are not reflected from thebeamsplitter configuration.
 9. The optical device of claim 8, wherein adifference between a length of the third and fourth optical paths variesas a function of an angle of incidence of the incoming light beam. 10.The optical device of claim 1, wherein each of the first prism and thesecond prisms has a geometric shape, and wherein the geometric shape ofthe first prism or the second prism is obtained from the second prism orthe first prism by performing at least one of scaling, translating,rotating, or reflecting to the second prism or the first prism.
 11. Theoptical device of claim 1, wherein the first prism is a reflectedversion of the second prism.
 12. The optical device of claim 1, whereinthe first surface of the first prism, the second surface of the firstprism, and the third surface of the first prism form a first triangle ina plane, and wherein the first surface of the second prism, the secondsurface of the second prism, and the third surface of the second prismform a second triangle in the plane, and wherein the first prism has astructural relationship to the second prism such that the first triangleis a scaled version of the second triangle.
 13. The optical device ofclaim 1, wherein the interface region extends along a majority portionof the second surface of the first prism and a majority portion of thesecond surface of the second prism, and wherein the majority portionsare equally sized portions.
 14. The optical device of claim 1, whereinthe interface region extends along a majority portion of the secondsurface of the first prism and a majority portion of the second surfaceof the second prism, and wherein the majority portions are unequallysized portions.
 15. The optical device of claim 1, wherein the interfaceregion extends along a majority portion of the second surface of thefirst or second prism, and wherein the interface region extends alongthe entirety of the second surface of the second or first prism.
 16. Anoptical device comprising: a prism assembly including: a first prismcomprising a light-transmitting material having a plurality of surfacesincluding at least a first surface associated with a source of light anda second surface oblique to the first surface, and a second prismcomprising a light-transmitting material having a plurality of surfacesincluding at least a first surface associated with a detector and asecond surface oblique to the first surface of the second prism, whereinthe second surface of the first prism is in overlapping relation withthe second surface of the second prism to define an interface region ofa given length that partially extends along at least one of the secondsurface of the first prism or the second surface of the second prism,and wherein the first and second prisms are optically attached at theinterface region; and a beamsplitter configuration overlying theinterface region, wherein an incoming light beam emitted by the sourceof light is transmitted by the beamsplitter configuration and issubsequently reflected by the beamsplitter configuration so as topropagate through the prism assembly along a first optical path to thedetector, and wherein the incoming light beam is reflected by thebeamsplitter configuration and is subsequently transmitted by thebeamsplitter configuration so as to propagate through the prism assemblyalong a second optical path to the detector, such that the incominglight beam reaches the detector as two coherent light beams, and whereineach of the first prism and the second prisms has a geometric shape, andwherein the geometric shape of the first prism or the second prism isobtained from the second prism or the first prism by performing at leastone of scaling, translating, rotating, or reflecting to the second prismor the first prism.
 17. An optical device comprising: a prism assemblyincluding: a first prism comprising a light-transmitting material havinga plurality of surfaces including at least a first surface associatedwith a source of light and a second surface oblique to the firstsurface, and a second prism comprising a light-transmitting materialhaving a plurality of surfaces including at least a first surfaceassociated with a detector and a second surface oblique to the firstsurface of the second prism, wherein the second surface of the firstprism is in overlapping relation with the second surface of the secondprism to define an interface region of a given length that partiallyextends along at least one of the second surface of the first prism orthe second surface of the second prism, and wherein the first and secondprisms are optically attached at the interface region; and abeamsplitter configuration overlying the interface region, wherein anincoming light beam emitted by the source of light is transmitted by thebeamsplitter configuration and is subsequently reflected by thebeamsplitter configuration so as to propagate through the prism assemblyalong a first optical path to the detector, and wherein the incominglight beam is reflected by the beamsplitter configuration and issubsequently transmitted by the beamsplitter configuration so as topropagate through the prism assembly along a second optical path to thedetector, such that the incoming light beam reaches the detector as twocoherent light beams, and wherein the first prism is a reflected versionof the second prism.